The since-closed waterslide used rafts that made the 17-storey drop at speeds of up to 110 kilometres per hour, followed by a surge over the hump and a 15-metre descent to a finishing pool.

Caleb was in a raft that went airborne and slammed him into a metal pole supporting a net meant to keep riders from flying off the slide.

Two women on the raft also were injured.

Prosecutors alleged that Mr Hughes and Mr Zalsman failed to replace a brake mat that fell off the slide two weeks earlier but told investigators that the mat had only been on the slide during testing phases.

Prosecutors said video evidence showed that the mat was used after the ride opened to customers in 2014.

“This was not a mistake, this was intentional calculated conduct,” said Adam Zentner, assistant Kansas Attorney General.

The defence said prosecutors did not understand how the slide functioned and questioned the testimony of Jason Diaz, the Kansas Bureau of Investigation agent who interviewed the defendants.

The defence also noted that another Schlitterbahn employee who made false statements to investigators was not charged.

“These are just two good old boys, they’re hard-working guys and because they’re the only two adults in the room they get singled out and have to get charged,” said Scott Toth, defence attorney for Hughes, as he addressed jurors.

Diaz said he did not believe the other employee had intentionally misled him.

Schlitterbahn has said the company had no reason to believe any employee obstructed justice.

“We have maintained our belief in the integrity of our staff and respect the process and decision by the jury,” Winter Prosapio, spokeswoman for Texas-based Schlitterbahn, said in a statement after the verdict.

The most serious charges in Caleb’s death have been filed against one of Schlitterbahn’s owners, Jeff Henry, Verruckt designer John Schooley and general contractor Henry & Sons Constructions.

Each is charged with second-degree murder, which carries up to 41 years in prison, aggravated battery, and aggravated endangerment of a child. Another employee is charged with involuntary manslaughter.

They have all pleaded not guilty. Their trials have not yet been scheduled.

The slide was shut down after Caleb was killed.

Caleb’s father Scott Schwab, a Republican from the Kansas City suburb of Olathe, had no immediate comment after being informed of the verdict on Thursday.

His son’s death prompted Kansas politicians to strengthen the state’s oversight of amusement park rides. Their 2017 law required amusement park rides to be inspected every year by a qualified inspector after previously allowing the parks to do their own.

The law also mandated that parks report injuries to the state.

But lawmakers quickly delayed criminal penalties for violations and then this year loosened rules further for county fairs and other short-term, one-location events run by non-profit groups. They also exempted attractions such as hay-rack rides.

The attorney general’s office did not respond to a message seeking comment.